There is normally nothing very difficult involved in takeoff,
climb, cruise from point to point, and descent solely by reference to instruments.
The complications arise when you must execute these maneuvers at precise
times, at specified altitudes, over designated routes and geographic positions,
and in an orderly sequence with other aircraft. An understanding of the
Air Traffic Control system will impress upon you the importance of the
training necessary for you to apply the proficiency you have acquired in
basic instrument flying and radio navigation techniques.

Federal regulation of civil aviation began with the Air Commerce
Act of 1926 and the creation of the Aeronautics Branch in the U.S. Department
of Commerce. The Department was concerned with the promotion of air safety,
licensing of pilots, development of air navigation facilities, and issuing
of flight information. Until the volume of air traffic increased, there
was no need for air traffic control, since the likelihood of aircraft colliding
in flight was remote.

The need for controlling air traffic was recognized in the 1930's
as the aviation industry produced bigger, faster, and safer aircraft, and
air transportation became an accepted mode of public travel. A number of
large cities, concerned with regulating the increasing air traffic at their
airports, built control towers and inaugurated a control service on, and
in the immediate vicinity of, the airports. Airline companies, eager to
expand and improve their operations, established control centers at Cleveland,
Chicago and Newark to provide their pilots with position and estimated
time of arrival information during instrument flights between those cities.

In 1936, the Federal Government assumed the responsibility for
operation of the centers, employing eight controllers. As aviation has
grown, so have the Federal Government functions and the agency charged
with the promotion and safety of civil aviation. By the late 1970's, approximately
25,000 ATC personnel provided direction and assistance to over 100 million
flights annually.

The number of active aircraft has increased from 29,000, all flying
at relatively slow and uniform speeds, to more than 200,000 aircraft operating
at various speeds ranging to more than 1,000 miles per hour. The aerial
highways have expanded from a few intercity routes to more than 250,000
miles of very high frequency routes utilizing approximately 1,000 VOR and
VORTAC stations. A continued increase in traffic volume is expected during
the coming decade.

The difficulties associated with mixed IFR and VFR traffic and
with diverse pilot training and varying aircraft capabilities, the trend
toward automated electronic equipment, and other aspects of control will
have a profound effect on flight operations, under both Visual and Instrument
Flight Rules.

As an instrument pilot normally operating under the jurisdiction
of Air Traffic Control, your understanding of the present system and its
operation will better enable you to make full use of ATC services.

Structure and Functions of Air Traffic Service

Air Traffic Service of FAA is responsible for three major general
functions: developing plans, establishing standards, and implementing systems
for control of air traffic. The two specific functions of immediate concern
to the instrument pilot are:

1. Providing preflight and inflight service to all pilots.
2. Keeping aircraft safely separated while operating in controlled
airspace.

The preflight and inflight services to pilots are the responsibility
of the Flight Service Stations (FSS). An extensive teletype and interphone
system permits relay of information from many sources. Many of the services
provided by tower and flight service personnel are familiar to the VFR
pilot. Aircraft separation is the primary responsibility of both Airport
Traffic Control Towers and Air Route Traffic Control Centers (ARTCC). Knowledge
of the physical setup and services provided by each type of facility enables
the instrument pilot to get information and assistance and to communicate
with the appropriate controllers with confidence and efficiency.

Airport Traffic Control Towers

Jurisdiction. The ATC tower is responsible for control of aircraft
on and in the immediate vicinity of airports. Terminals handling a large
traffic volume employ specialized personnel for operations; they use light
signals, radio, and ASDE radar (Airport Surface Detection Equipment) for
control of surface traffic. Less congested airports have fewer controllers
to handle the workload with less specialization.

Organization of the tower operations falls into the following
units:

Local Control is concerned mainly with VFR traffic in and around
the traffic pattern and with ground traffic. The local controller works
with the other IFR controllers to integrate VFR and IFR flights into a
smooth, safe traffic flow in and out of the airport.

Ground Control directs the movement of aircraft on the airport
surface, working closely with other tower positions. The controller relays
clearances from ARTCC to departing IFR flights unless a special position
is assigned that function.
Clearance Delivery is accomplished by a separate controller
at most busy terminals where heavy ground traffic and frequent IFR departures
require division of the workload.

Departure Control originates departure clearances and instructions
to provide separation between departing and arriving IFR flights. Although
the physical location of this controller varies at different terminals
- in the tower at some locations, in separate radar installations at others
- there is a close coordination with the Approach Controller and Local
Controller.

Approach Control formulates and issues approach clearances and
instructions to provide separation between arriving IFR aircraft, using
radar if available.

Tower Services Provide:
1. Control of aircraft on, and in the vicinity of the airport.
2. Coordination with pilots and Air Route Traffic Control Centers
for IFR clearances.
3. Air traffic advisories to pilots concerning observed, reported,
and estimated positions of aircraft that might present a hazard to a particular
flight.
4. Flight assistance, including transmission of pilot reports
and requests, and weather advisories.

Approach/departure Control Services Provide:
1. Navigation assistance by radar vector for departing and arriving
aircraft.
2. DF assistance to lost aircraft, and cooperation with other
facilities in Search and Rescue operations.
Some of the larger towers have more than one of the above described
positions of operation, each position having its area of responsibility
on, or in the vicinity of, the airport. Also, the APPROACH CONTROL function
at some highly complex multi-airport metropolitan areas has been established
separate from and serving several major or less busy airports.

Air Route Traffic Control Centers

Jurisdiction. The primary function of an ARTCC is to provide air
traffic control service to aircraft operating on IFR flight plans within
controlled airspace, principally during the enroute phase of flight. When
equipment capability and controller workload permit, certain advisory/assistance
services may be provided to VFR aircraft.

Organization. The ARTCC facilities are located throughout the
United Sates at central points in areas over which they exercise control.
Each Center controls IFR traffic within its own area and coordinates with
adjacent Centers for the orderly flow of traffic from area to area. Each
Center's control area is divided into Sectors, based upon traffic flow
patterns and controller workload.

Each Sector Controller normally has a sector discrete frequency
for direct communications with IFR flights within the sector. As an IFR
flight departs, the affected Sector Controller follows the progress of
the flight, maintaining a continuing record of route, altitude, and time,
and monitors the flight with long-range radar equipment when available.
Each Sector Controller has a sector discrete frequency for direct communication
with IFR flights within the sector. As an IFR flight progresses to adjacent
sectors and centers, and finally to the destination terminal facility,
the IFR pilot is requested to change to appropriate frequencies.

The chief functions of the Air Route Traffic Control Centers are
to: (1) control aircraft operating under IFR in controlled airspace, (2)
provide air traffic advisories to aircraft concerning potential hazards
to flight, anticipated delays, and any other data of importance to the
pilot for the safe conduct of the flight, (3) provide navigation assistance
by radar vectors for detouring thunderstorms and expediting routing, (4)
transmit pilot reports and weather advisories to enroute aircraft, and
(5) provide flight assistance to aircraft in distress.

Air Traffic Control Automation

NAS Enroute Stage A

This term refers to ATC's automation of the routine tasks of enroute
traffic control through the use of computers. The automation is being accomplished
in two phases, the flight data processing phase and the radar data processing
phase. In the flight data processing phase, the computer takes over the
task of processing, printing, distributing, and updating flight plans.
In the past, controllers have performed these clerical chores.

The radar data processing phase of enroute automation involves
bringing vital information about each flight to the radar scope. The controller
formerly transferred control information from the flight progress strips
to plastic markers called "shrimp boats." These "shrimp boats" were manually
kept in association with the displayed radar targets. The controller had
to remember which flight progress strip applied to each radar target and
"shrimp boat" on the scope - a process which called for heavy concentration
and constant verification. Through an electronic process, the computer
converts digital information into letters and numbers and projects a bright
tag containing all necessary flight data on the radar scope. This alphanumeric
display includes flight identification, assigned altitude, Mode C altitude,
computer identification, and a special field that includes control data.
Whether an aircraft is climbing or descending is also graphically shown
by an arrow pointing up or down. The data tag is attached to the radar
target of each aircraft being controlled. A controller "hands of" an aircraft
to another controller by making a keyboard entry to the computer, causing
the data tag to transfer to the new controller's scope. The tag blinks
until the new controller acknowledges the handoff. The Mode C altitude
readout is accomplished through the aircraft's transponder and encoding
altimeter.

ARTS III

This automated system provides controllers at medium and high
activity terminal facilities information similar to NAS Enroute Stage A.
This includes the display of aircraft flight data and automated handoff
capability within the terminal facility with other ARTS-III facilities
and with NAS Enroute Stage A.

New programs have been added to the system such as Minimum Safe
Altitude Warning (MSAW) and Conflict Alert. The former alerts the controller
when a controlled aircraft is below or is predicted to descend below a
minimum designated altitude or minimum descent altitude (MDA) if past the
final approach fix. The latter alerts the controller to unsafe or potentially
unsafe proximity between controlled aircraft. These alerts are in the form
of a warning message displayed blinking on the controller's radar display
accompanied by an aural alarm.